tunefs(1M)tunefs(1M)NAMEtunefs - tune up an existing HFS file system
SYNOPSIS
maxcontig] rotdelay] maxbpg] minfree]
advanced read-ahead] special-device
DESCRIPTION
The command is used to alter dynamic parameters that affect HFS file
system layout policies. Parameters to be altered are specified by the
options and arguments provided on the command line as described below.
affects how the file system blocks are laid out on the disk. The
default rotdelay value set by the and commands (see newfs(1M) and
mkfs(1M)) is 0 milliseconds, causing file system blocks to be written
and read consecutively. In general, this should be the optimal tuning,
making the use of unnecessary.
Options
recognizes the following options and command-line arguments:
Set the maximum number of contiguous blocks that will be laid
out
before forcing a rotational delay to maxcontig
(see below). The default value is because most
device drivers require one interrupt per disk
transfer. For device drivers that can chain sev‐
eral buffers together in a single transfer, set
maxcontig to the maximum chain length.
rotdelay is the expected time (in milliseconds) to service
a transfer completion interrupt and initiate a
new transfer on the same disk. It is used to
determine how much rotational spacing to place
between successive blocks in a file.
maxbpg specifies the maximum number of blocks any single
file can allocate out of a cylinder group before
it is forced to begin allocating blocks from
another cylinder group. Typically this value is
set to about one fourth of the total blocks in a
cylinder group. The intent is to prevent any
single file from using up all the blocks in a
single cylinder group, thus degrading access
times for all files subsequently allocated in
that cylinder group. The effect of this limit is
to cause large files to do long seeks more fre‐
quently than if they were allowed to allocate all
the blocks in a cylinder group before seeking
elsewhere. For file systems with exclusively
large files, this parameter should be set higher.
minfree specifies the percentage of space that is not
available to normal users; i.e., the minimum free
space threshold. The default value used is 10%.
This value can be set to zero. If set to zero,
throughput performance drops to as little as one-
third of the efficiency expected when the thresh‐
old is set at 10%. Note that if minfree is
raised above the current usage level, users can‐
not allocate files until enough files have been
deleted to meet the new threshold requirement.
Advanced read-ahead
specifies whether the file system should use an
advanced predictive read-ahead algorithm. The
implementation requires more system resources in
exchange for an advanced access pattern recogni‐
tion. Patterns include forward sequential, back‐
ward sequential, forward strided, and backward
strided. This value can be set to zero (disable)
or one (enable). By default, a file system will
have advanced read-ahead enabled when created.
(visual) Display current values
contained in the primary super-block to standard
output.
(all) Modify redundant super-blocks as well as the primary
super-block
as stipulated by the configuration options and
arguments.
special-device is the name of the file system to be tuned. It
is either a block or character special file if
the file system is not mounted, or a block spe‐
cial file if the file system is mounted.
WARNINGS
Root file system tuning is normally done during initial system software
installation. Tuning the root file system after installation has lit‐
tle useful effect because so many files have already been written.
AUTHOR
was developed by the University of California, Berkeley.
SEE ALSOdumpfs(1M), mkfs(1M), newfs(1M).
tunefs(1M)
